1. Field of the Invention
The invention is generally related to an optical device and a light source, and more particularly, to a light guide plate and a light source module.
2. Description of Related Art
A conventional side incident type light source module employs a light guide plate to guide a light beam emitted by a light emitting device disposed besides the light guide plate, to a front surface of the light guide plate, so that a planar light source is formed. Generally, after the light beam emitted by the light emitting device is guided from a side surface of the light guide plate into the light guide plate, the light beam is totally reflected continually by the upper and lower surfaces of the light guide plate, and thereby the light beam is restricted within the light guide plate. However, microstructures disposed on a surface of the light guide plate may destroy the total reflection effect, such that the light beam is incident upon the upper surface with an incident angle of less than a critical angle, and the light beam transmits through the upper surface.
Although the microstructures may destroy the total reflection, a majority of the light beams is obliquely emitted out of the upper surface due to the microstructures, instead of being directly forward emitted out of the upper surface. In order to promote forward emission of the light beams, a prism sheet is typically disposed on the upper surface of the light guide plate of the conventional light source module, so as to direct a light path of the light beams towards one emitting direction approaching a forward and frontal direction. Moreover, the prism sheet totally reflects a portion of light beams having particular advancing angles back towards the light guide plate to reuse the light beams. However, a light loss occurs when the light beams pass through a prism sheet and when the light beams are totally reflected back towards the light guide plate, thereby lowering a brightness provided by the light source module.
Taiwan Patent No. I282021 disclosed a light guide plate with microstructures, wherein the microstructures are arranged repetitiously on a bottom surface of the light guide plate. Taiwan Patent No. I296352 disclosed a light guide plate having multi-layered ring-shaped structures. The light guide plate has a first ring-shaped microstructure and a second ring-shaped microstructure. The first and second ring-shaped microstructures have different bottom surface widths. The microstructures may be disposed on a lower surface of the light guide plate. On the other hand, U.S. Pat. No. 6,454,452 disclosed a light guide plate with a bottom surface having wedge-shaped grooves, wherein an included angle of the grooves between an inclined surface and the bottom surface may be 43°, 45°, and 47°. Taiwan Patent No. M321111 disclosed a light guide plate having regularly arranged microstructures. U.S. Pat. No. 6,612,722 disclosed a light guide plate having microstructures. Moreover, U.S. Pat. No. 6,834,973 disclosed a light guide plate with a bottom surface having micro-reflector structures.